IS-IS Support for an IS-IS Instance per VRF for IP

This feature provides multiple VRF-aware IS-IS instances. The VRF functionality allows Internet service providers (ISPs) to separate routing protocol information and propagate it to the appropriate routing table and network neighbors. Using one router with VRF functionality is more cost-effective than using separate routers to separate and forward the routing information.

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Prerequisites for IS-IS Support for an IS-IS Instance per VRF for IP

It is presumed that you are running IS-IS on your network.

The VRF configuration is a prerequisite to associating an IS-IS instance with that specific VRF. However, the VRF configuration is independent of associating it with IS-IS or any other routing protocol. An IS-IS instance cannot be referred to as being VRF-aware until it has been associated with a particular VRF.

Restrictions for IS-IS Support for an IS-IS Instance per VRF for IP

Support for IS-IS VRF is provided only for IPv4.

When you configure the IS-IS Support for an IS-IS Instance per VRF for IP feature, you must comply with the following nine best-practice guidelines:

IS-IS instances running Connectionless Network Services (CLNS) must have the same system ID.

An IS-IS instance that is running CLNS or IPv6 cannot be associated with a VRF.

You can configure only one IS-IS instance to run both CLNS and IP.

IS-IS instances within the same VRF must have unique system IDs, although IS-IS instances located in separate VRFs can have the same system ID.

You can associate an IS-IS instance with only one VRF.

You can configure the passive-interfacedefault command only on one IS-IS instance per VRF.

Redistribution is allowed only within the same VRF.

You can enable only one IS-IS instance per interface.

An interface can belong to an IS-IS instance only if it is associated with the same VRF.

Note

If you are using LDP, you cannot use the route-target command when configuring a VRF. The router will use BGP for Multiprotocol Label Switching (MPLS) labels.

Information About IS-IS Support for an IS-IS Instance per VRF for IP

VRF-Aware IS-IS

You can configure IS-IS to be VPN routing and forwarding (VRF)-aware. A VRF consists of an IP routing table, a derived Cisco Express Forwarding (CEF) table, a set of interfaces that use the forwarding table, and a set of rules and routing protocol parameters that control the information that is included in the routing table.

IS-IS Support for an IS-IS Instance per VRF for IP Feature Operation

ISPs have the capability to create multiple VRF-aware IS-IS instances that run on one router, rather than requiring duplicate hardware. IS-IS can be enabled to be VRF-aware, and ISPs can use multiple VRF-aware IS-IS instances to separate customer data while propagating the information to appropriate service providers.

For example, an ISP can create three VRFs--VRF First, VRF Second, and VRF Third--to represent three separate customers. A VRF-aware IS-IS instance is created and associated with each VRF: tagFIRST, tagSECOND, and tagTHIRD. Each instance will have its own routing process, IS-IS database, and routing table, and will calculate its own shortest path first (SPF) tree.

Creating VRF-Aware IS-IS Instances

Prerequisites

Before you create VRF-aware IS-IS instances, you need to enable IP routing on the router.

Note

Only one instance within the VRF can be configured as the passive interface default.

Creating a VRF-Aware IS-IS Instance in Interface Configuration Mode

SUMMARY STEPS

1.enable

2.configureterminal

3.interfacetypenumber

4.ipaddressip-addressmask [secondary]

5.iprouterisisprocess-tag

6.noshutdown

7.end

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

interfacetypenumber

Example:

Router(config)# interface GigabitEthernet 0/2/0

Configures an interface type and enters interface configuration mode.

Step 4

ipaddressip-addressmask [secondary]

Example:

Router(config-if)# ip address 172.16.11.1 255.255.255.255

Sets a primary or secondary IP address for an interface.

Step 5

iprouterisisprocess-tag

Example:

Router(config-if)# ip router isis tagfirst

Configures an IS-IS routing process for IP on an interface and attaches a tag to the routing process.

Note

The configuration of the interface-mode iprouterisis command will overwrite the prior configuration on that interface, but only if the new configuration is attempting to change the interface ownership to a different instance that is in the same VRF as the currently configured owner instance. The configuration will be rejected if the attempted change is between two instances that are associated with different VRFs.

A new IS-IS instance with the process tag tagThird will automatically be created and associated with the VRF Third. When the showrunning-config command is entered, the following information for the new IS-IS instance will be displayed:

Example Creating an IS-IS Instance Without a Process Tag

In the following example, an IS-IS instance was created without the optional process tag. When an IS-IS instance is created without the optional process tag, you can display its information by entering the commands such as showclnsprotocol with "null" specified for the process-tag argument.

Example Redistributing Routes from an IS-IS Instance

In the following sample configuration, routes have been redistributed from the IS-IS instance "null" into the IS-IS instance named tagBLUE. Routes from an OSPF process in VRF Blue have been redistributed into the IS-IS instance named tagBLUE.

Example Changing the Interface Ownership

In the following sample configuration, POS interface 6/1/0 was originally enabled for IS-IS IP routing for a "null" instance that does not have a process tag, which is in vrfSecond. The new configuration changes the ownership of POS interface 6/1/0 to another instance tagSecond, which is also in vrfSecond.

Note

Note that use of the iprouterisiscommand in interface configuration mode will overwrite the prior configuration on that interface, but only if the new configuration is attempting to change the interface ownership to a different instance that is in the same VRF as the currently configured owner instance. The configuration will be rejected if the attempted change is between two instances that are associated with different VRFs.

RFCs

RFCs

Title

No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.

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Link

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Feature Information for IS-IS
Support for an IS-IS Instance per VRF for IP

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to
www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

Table 1 Feature Information for IS-IS
Support for an IS-IS Instance per VRF for IP

Feature
Name

Releases

Feature
Information

IS-IS
Support for an IS-IS Instance per VRF for IP

Cisco IOS
XE Release 2.1

Cisco IOS XE Release 3.3SG

Cisco IOS XE Release 3.5E

This
feature provides multiple VRF-aware IS-IS instances. The VRF functionality
allows ISPs to separate routing protocol information and propagate it to the
appropriate routing table and network neighbors. Using one router with VRF
functionality is more cost-effective than using separate routers to separate
and forward the routing information.

This
feature was introduced on the Cisco ASR 1000 Series Aggregation Services
Routers.

The
following commands were modified by this release:
showclnsneighbors,
showclnsprotocol,showisisdatabase,showisistopology,vrf(routerconfiguration)